Transplantation of cells is being utilized therapeutically from bone marrow transplants to neural cell transplants. Improved means to facilitate such cellular transplants are needed, particularly where differentiated cells are being transplanted. These cells cannot be cultured to increase cell number so preservation of viability for transplant is critical.
Transplantation protocols can include the infusion of cells from a donor. For example, in some cancer therapies a patient's bone marrow is removed, and then reinfused following high dose chemo- and/or radiation therapies. It would be useful to have improved methods of preserving such cells. In other cases, bone marrow donors are not available from relatives and must be matched from the national registry. It would be useful to be able to have preserved such cells rather than having to find the donor at the time the cells are needed. Therefore, improved methods of cryopreservation are needed since a substantial portion of cryopreserved cells are not viable upon thawing.
In addition, hybridomas are stored utilizing cryopreservation. Improved methods for preserving hybridomas with increased viability would be useful.
As a further example, the central nervous system (CNS) (brain and spinal cord) has poor regenerative capacity which is exemplified in a number of neurodegenerative disorders. An example of such a disorder is Parkinson's disease. The preferred pharmacotherapy for Parkinson's disease is L-dopa which helps the symptoms of this disease in humans. However, the neuropathological damage and the debilitating progression is not reversed by this treatment protocol.
Laboratory and clinical studies have shown the transplantation of cells into the CNS is a potentially significant alternative therapeutic modality for neurodegenerative disorders such as Parkinson's disease (Wictorin et al., 1990; Lindvall et al., 1990; Sanberg et al., 1994; Bjorklund and Stenevi, 1985; Freeman et al., 1994). In some cases, transplanted neural tissue can survive and form connections with the CNS of the recipient i.e. the host (Wictorin et al., 1990). When successfully accepted by the host, the transplanted tissue (i.e. the graft) has been shown to ameliorate the behavioral deficits associated with the disorder (Sanberg et al., 1994). The obligatory step for the success of this kind of treatment is to have viable cells available for the transplant.
Currently, fetal neural tissue is the primary graft source for neural transplantation (Lindvall et al., 1990; Bjorklund, 1992; Isacson et al., 1986; Sanberg et al., 1994). Other viable graft sources include adrenal chromaffin cells and various cell types that secrete neural growth factors and trophic factors. The field of neural tissue transplantation as a productive treatment protocol for neurodegenerative disorders has received much attention resulting in its progression to clinical trials. Preliminary results and clinical observations are promising but obtaining viable cells remains a problem.
Recently, studies have suggested that Sertoli cells, when simultaneously transplanted with pancreatic islet cell into the diabetic rat, act as an effective local immunosuppressant on the host tissue (Selawry and Cameron, 1993). As a result, the graft is not rejected and the islets remain viable allowing the transplanted .beta.-cells to function normally and produce insulin for an indefinite period of time. As a result, the accepted graft overcomes the primary physiological dysfunction of hyperglycemia thereby alleviating the related complications of this endocrine disorder. This cell transplantation protocol is accomplished without prolonged systemic immunosuppression, otherwise necessary when islets are transplanted without Sertoli cells.
In general, systemic immunosuppression is necessary if successful transplantation is to be achieved in humans. Immunosuppression of the entire body (i.e. systemic) can result, eventually, in graft acceptance. It is acquired, however, by placing the individual at medical risk making the immunosuppressant therapy itself more of a liability than a benefit in some cases. For a lack of a better immunosuppressant treatment, systemic immunosuppressants, with Cyclosporine-A (CsA) as the treatment choice, have been used as adjunctive therapy in neural transplantation protocols (Sanberg et al., 1994; Freeman et al., 1994; Borlongan et al., 1995). Arguably, systemic CsA treatment may be contraproductive to successful graft acceptance in the CNS because of its systemic effect and because CsA itself has been shown to cause detrimental side effects and may, in fact, be cytotoxic to neural tissues (Berden et al., 1985; de Groen et al., 1984).
It would be desirable to enhance the productive cell transplantation techniques already utilized for neurodegenerative disorders, such as Parkinson's disease, and other types of disorders in ways which would more effectively slow the neurodegenerative disease process, more actively promote the re-establishment of normal neural tissue physiology and better alleviate the functional disabilities associated with the neural tissue dysfunction.
Cell transplantation therapies are optimized by the availability of cryopreserved cells which have high viability. Transplantable cells, such as fetal brain cells, do not withstand cryopreservation well. Therefore, it would be desirable to have a method for enhancing the preservation and viability of cryopreserved cells in order to optimize the function of the cells and to obtain the resultant benefits to the transplant recipient.